1. Field of the Invention
This invention relates to shaft end couplings for dynamoelectric machines. More particularly, this invention relates to a keyed arrangement for maintaining the alignment of a dynamoelectric machine rotor shaft and a coupling member shrink fitted onto that shaft.
2. Description of the Prior Art
In mechanically connecting rotor shafts of dynamoelectric machines and prime movers such as turbines, coupling members are fixed to both shafts and mechanically connected together as by bolts or other devices well known in the art. It has been the practice to maintain the alignment of the coupling members with the corresponding shafts by keying the two elements together with two keys comprising elongated members of square or rectangular cross section. Prior to assembly, mating grooves are machined in the rotor shaft and the coupling member separately. The coupling member is then shrink fitted on the shaft such that the grooves in the shaft mate with the corresponding grooves in the coupling member. To complete the assembly, the keys are inserted in keyways formed by the mating grooves in the shaft and coupling member. The limitation to only two keys in such prior art couplings was necessitated by the difficulty involved in the alignment of these grooved members in the shrink fitting operation. The magnitude of such difficulties increases with an increased number of keys. Therefore, it is necessary to provide over-sized keyways in these elements so that should such misalignment occur, the keys may still be accommodated in the keyways.
This difficulty in aligning two grooves to form a keyway is one of a number of disadvantages associated with such prior art keying arrangements. Since only two solid rectangular keys are used in prior art couplings, it is necessary that such keys and the corresponding coupling member be of relatively great length to provide the required strength. However, this large key length has associated with it a large coupling weight which may cause lateral shaft resonance at normal operating speeds damaging the shaft and various members fixed thereto. The use of only two keys makes it necessary that such keys be formed from high strength steel which upon shearing of the keys may damage the shaft and the coupling member. Moreover, solid rectangular keys are relatively inelastic. Thus, when excessive torque is applied to the shaft through the coupling member, the keys fail without distorting elastically and without accommodating the excessive torque. Finally, the sharp corners of the grooves machined in the shaft and coupling member to accommodate keys of square or rectangular cross section define areas of high stress concentration. The presence of such areas has a weakening affect on the shaft.
It is therefore an object of this invention to provide a novel and improved keying arrangement for use in dynamoelectric machine or turbine couplings which has assocated with it accommmodating keyways in a shaft and coupling member formed from grooves which are incapable of being misaligned.
It is another object of this invention to provide a novel and improved keying arrangement for use in dynamoelectric machine or turbine couplings characterized by low cost and ease of manufacture.
It is another object of this invention to provide a novel and improved keying arrangement for use in dynamoelectric machine or turbine couplings which is characterized by a relatively short length and thus permits utilization of a relatively light-weight associated coupling member thereby preventing lateral shaft resonance at operating speeds.
It is another object of this invention to provide a keying arrangement for a dynamoelectric machine or turbine coupling utilizing keys made from a relatively low strength material which will not damage the shaft or coupling member in the event of a failure of the coupling.
It is another object of the present invention to provide a keying arrangement for a dynamoelectric machine or turbine coupling which will elastically distort when excessive torque is applied to the coupling, preventing the shearing of the keys under such conditions.
It is another object of the present invention to provide a keying arrangement for a dynamoelectric machine or turbine coupling having associated with it keys and accommodating grooves in the shaft and coupling member which have no sharp corners.